THE BRITISH JOURNAL OF PHOTOGRAPHY. May 2, 1864. p146.
THE employment of weak silver baths is a subject with which the whole photographic world is now occupied. The practical photographer very justly seeks to diminish his working expenses by economising his silver. On a former occasion, when giving some instructions in the use of albumenised paper, we pointed out the very great risk incurred by a photographer, deficient in chemical knowledge, using weak silver baths--a risk which might entail the entire failure of a day's work, and thus cost far more than the employment of the very strongest silver solution; so that it was not without due deliberation that we coupled with our instructions the advocacy of a strong bath. It is beyond question that a photographer who possesses a practical knowledge of chemistry and understands the properties of the chemicals he is employing will be able to produce good prints on our or any other well-manufactured paper with a solution of twenty grains to the ounce. But then he must bear in mind that each sheet of sensitised paper considerably impoverishes his solution of four-five per cent strength, and he is therefore careful to continually make good the loss, since he is well aware that, in sensitising the albumenised paper, it is not sufficient to obtain a film of mere chloride of silver (which would yield prints with cold, flat tones); but that, to get a rich, warm print, he must allow sufficient silver for the albumen film to become completely coagulated with it, in addition to the formation of the chloride of silver film, and that the organic combination (so well known to photographic experimentalists) of albumen With oxide of sub oxide of silver must be formed which only in connection with chloride of silver is capable of producing the results he desires.
Indeed, the methods of economising silver that have hitherto been propose have only aimed at coagulating the albumen film of the paper, or rendering it insoluble without expending silver thereon, as, for instance, the addition of acetate or nitrate of lead, which, what ever may be said to the contrary by some experimentalists whose names rank high in the photographic world, is always done at the expense of the brilliancy of tone of the print. Moreover, we think it probable that we shall be obliged to regard most of the metallic additions to the printing bath as more or less useless, since in the majority of them the silver will show a greater chemical affinity for the albumen, and will either force them out of their combination with albumen, where such has already taken place, or will prevent the formation of such a combination; so that in a silver bath prepared with additions of foreign metals there would at least be formed a mixture of silver, lead, and other albuminates, about the sensitiveness of which, and consequent utility for the print, there is still nothing known. It may reasonably be supposed that but few of them are sensitive.
The addition of nitrate of soda--by which many affirm they have effected a considerable saving of silver--acts only by impregnating to a certain extent the water of the silver bath with particles of matter, and thus mechanically preventing the solution of the albumen film, which would else, with a very weak silver solution, be inevitable. Nevertheless, this addition is far more dangerous than that of metallic salts, for every physiological chemist is aware that bodies containing albumen are much more soluble in weak solutions of the neutral salts of alkalies than in pure water; if, therefore, such silver solutions were not at least safer saturated with nitrate of soda, &c., the very opposite result to that desired might easily follow, and, finally, picture, albumen, &c., would be swimming at the bottom of the bath. It is true most photographers would in such a case soon decide upon rejecting both paper and chemicals as unfit for use, without thinking it worth while to give them a more careful trial; yet this much is certain, that all these experiments made by renowned photographers will remain-as much dead matter (although very valuable) so long as we are not in a position to ascertain from them exactly how long they have worked with weak baths, and how long such baths have produced good pictures: in such a case one or two copies prove little or nothing.
We shall endeavour, in the succeeding series of articles; to support the opinions to which we have given expression above by easily intelligible proofs and experiments.E. SCHERING.
(To be continued.)